From 7b15523a989b63927c2bb08e9b5b0bbc10b58bef Mon Sep 17 00:00:00 2001 From: Florent Revest Date: Mon, 19 Apr 2021 17:52:40 +0200 Subject: bpf: Add a bpf_snprintf helper The implementation takes inspiration from the existing bpf_trace_printk helper but there are a few differences: To allow for a large number of format-specifiers, parameters are provided in an array, like in bpf_seq_printf. Because the output string takes two arguments and the array of parameters also takes two arguments, the format string needs to fit in one argument. Thankfully, ARG_PTR_TO_CONST_STR is guaranteed to point to a zero-terminated read-only map so we don't need a format string length arg. Because the format-string is known at verification time, we also do a first pass of format string validation in the verifier logic. This makes debugging easier. Signed-off-by: Florent Revest Signed-off-by: Alexei Starovoitov Acked-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20210419155243.1632274-4-revest@chromium.org --- include/linux/bpf.h | 1 + include/uapi/linux/bpf.h | 28 ++++++++++++++++++++++++++++ 2 files changed, 29 insertions(+) (limited to 'include') diff --git a/include/linux/bpf.h b/include/linux/bpf.h index c160526fc8bf..f8a45f109e96 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1953,6 +1953,7 @@ extern const struct bpf_func_proto bpf_skc_to_tcp_request_sock_proto; extern const struct bpf_func_proto bpf_skc_to_udp6_sock_proto; extern const struct bpf_func_proto bpf_copy_from_user_proto; extern const struct bpf_func_proto bpf_snprintf_btf_proto; +extern const struct bpf_func_proto bpf_snprintf_proto; extern const struct bpf_func_proto bpf_per_cpu_ptr_proto; extern const struct bpf_func_proto bpf_this_cpu_ptr_proto; extern const struct bpf_func_proto bpf_ktime_get_coarse_ns_proto; diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index df164a44bb41..ec6d85a81744 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -4708,6 +4708,33 @@ union bpf_attr { * Return * The number of traversed map elements for success, **-EINVAL** for * invalid **flags**. + * + * long bpf_snprintf(char *str, u32 str_size, const char *fmt, u64 *data, u32 data_len) + * Description + * Outputs a string into the **str** buffer of size **str_size** + * based on a format string stored in a read-only map pointed by + * **fmt**. + * + * Each format specifier in **fmt** corresponds to one u64 element + * in the **data** array. For strings and pointers where pointees + * are accessed, only the pointer values are stored in the *data* + * array. The *data_len* is the size of *data* in bytes. + * + * Formats **%s** and **%p{i,I}{4,6}** require to read kernel + * memory. Reading kernel memory may fail due to either invalid + * address or valid address but requiring a major memory fault. If + * reading kernel memory fails, the string for **%s** will be an + * empty string, and the ip address for **%p{i,I}{4,6}** will be 0. + * Not returning error to bpf program is consistent with what + * **bpf_trace_printk**\ () does for now. + * + * Return + * The strictly positive length of the formatted string, including + * the trailing zero character. If the return value is greater than + * **str_size**, **str** contains a truncated string, guaranteed to + * be zero-terminated except when **str_size** is 0. + * + * Or **-EBUSY** if the per-CPU memory copy buffer is busy. */ #define __BPF_FUNC_MAPPER(FN) \ FN(unspec), \ @@ -4875,6 +4902,7 @@ union bpf_attr { FN(sock_from_file), \ FN(check_mtu), \ FN(for_each_map_elem), \ + FN(snprintf), \ /* */ /* integer value in 'imm' field of BPF_CALL instruction selects which helper -- cgit v1.2.3